This invention relates generally to electrical switches, and more particularly to an electrical switch for large currents.
In conventional high voltage switches for large currents, the rated current is conducted through several contact elements connected in parallel in order to obtain the lowest possible contact resistance. During the opening operation of the switch as the switch moves in a make/break direction from a make-position in which a circuit is electrically closed to a break-position in which the circuit is electrically open, the current is commuted from a rated making current path to a power path. The inductance of the power path may create problems in commutating very large currents.
An electrical switch for large starting currents is disclosed in Federal Republic of Germany Patent No. 11 91 465. The switch disclosed therein includes a contact piece made from an elastic tube. A plurality of slits are inflicted on the tube in order to form a plurality of contact bars. The contact bars cooperate with a solid contact piece in the make-position of the switch in order to close the electrical circuit. The elasticity of the tube makes the contact bars self-loading, and urges the contact bars against the solid contact piece. Additional springs are also used to further urge the contact bars toward the solid contact piece.
The contact bars are essentially straight contact elements, and thus represent practically the shortest current path between the slit, elastic tube contact piece and the solid contact piece. However, during the closing operation of the switch as the switch is selectively operated from the break-position to the make-position the contact elements do not remain in physical contact with the solid contact piece once physical contact is made, but rather the contact elements bounce back and forth. This undesired contact bounce results in harmful burning of the contacts. The additional springs are provided in order to reduce the contact bounce and thereby reduce the burning. However, such an expedient deals only with problems arising during the closing operation of the switch, but not during the opening operation.
It is therefore an object of the present invention to improve the commutation of current from the rated making current path to the power path with a relatively uncomplicated switch structure.